ospC

OspC, or outer surface protein C, is a lipoprotein on the surface of Borrelia burgdorferi sensu lato, the spirochete that causes Lyme borreliosis. The ospC gene is carried on one of the bacterium’s plasmids, and the encoded protein is produced predominantly during the early stages of mammalian infection and during tick-to-mammal transmission.

Expression of OspC is developmentally regulated and linked to the tick feeding cycle. As the spirochete transitions from the tick to the host, ospA is downregulated and ospC is upregulated. In mammalian hosts, OspC contributes to establishment and early dissemination of infection, and experimental loss of function can reduce infectivity.

A defining feature of OspC is extensive genetic diversity. There are many ospC alleles (types), which differ among Borrelia strains and species. This allelic variation leads to strain-specific immune responses and presents challenges for serodiagnosis and vaccine design, as cross-protection between variants is limited.

Clinically, antibodies against OspC appear early in infection, making the protein a target of some early Lyme disease serology tests, typically used alongside other antigens. Research into OspC-based vaccines has shown potential but has been hampered by antigenic diversity, limiting broad protection across circulating strains. OspC-related diagnostics and vaccine approaches remain an area of active study.

OspC is discussed mainly in the context of Borrelia burgdorferi, but related Borrelia species can encode analogous outer surface lipoproteins that contribute to their pathogenic processes in respective hosts.